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Overview Statement: 

This page includes detailed, need-to-know, information for commercial/industrial water customers.

  • Is your water system at risk because of you?
  • Are you doing your part?
  • What’s the big deal?

What is a Cross Connection and what is Backflow?

Cross-Connection – is the physical connection between the potable (drinking) water system and an “end-use” (water utilizing fixture, equipment, or process) where a potential water contaminating hazard exists. Backflow – is the undesired reverse flow of contaminants into the potable water from an “end-use” hazard and is typically driven by common, but unfavorable, hydraulic events in either the public or a private water distribution system.

Explaining Cross Connection and Backflow Prevention A Comprehensive Informational Page

Responsible Party/Enforcement

The WSSC Water Plumbing Code ultimately designates the property owner as the responsible party for all water “end uses” on their property. However, WSSC Water staff is employing a more practical application of enforcement measures at the first level of follow-up. Backflow prevention devices and assemblies, as well as unprotected outlets, that were initiated (installed) under the control of a tenant fit-out shall be corrected, tested and/or  maintained, by the tenant. Other devices, assemblies, or unprotected outlets installed as part of a building or campus’s core/shared plumbing and mechanical systems, shall be corrected, tested and/or maintained by the property owner, property manager, owner’s agent, or landlord. WSSC Water reserves the right to escalate all unresolved enforcement actions to the property owner’s attention. Whereby water and/or sewer service are subjected to suspension when unsafe conditions persist and written directives and/or Notices of Violation remain unresolved.

Containment v. Isolation

Containment is the practice of placing a backflow preventer on an entire property, campus, or whole building. Isolation is the practice of placing a backflow preventer at the point of connection to an individual fixture, appliance, water utilizing equipment, or in some cases: a small group of like items. Over the most recent four decades, the plumbing code has mandated isolation based protection and only the highest of hazardous facilities were mandated to have containment protection in addition to isolation. Since 2007, all water customers are required to install both containment and isolation based protection.

Existing Systems (Grandfather clause)

All existing water “end use” applications shall be evaluated based on current industry best practices and code requirements. Due to the severity of health risk, existing applications cannot remain unabated or under-protected simply because they were potentially approved under some former version of code or potentially approved by a former inspector. Isolation protection shall be mandatory; adding containment protection to existing campuses or entire buildings will be mandated on a priority basis. See WSSC  Water Plumbing and Fuel Gas Code, Sections 502.3.2 & 502.3.3.


In general, WSSC  Water Submeters shall be installed upstream (ahead of), backflow prevention assemblies.

Various Commercial/Industrial Water “End Uses” (How do customers use their water?)

General (residential type) Plumbing Fixtures and Plumbing Appliances

Built-in Protection - Modern plumbing fixtures generally have built-in backflow protection. For instance, a faucet spout terminates above the flood rim level of the sink or tub. So if the sink or tub is full of dirty water or worse, backed-up sewage, there is no possible way for a backflow because of the air gap created by the elevated spout. Toilet fill valves, clothes washers, dishwashers, and refrigerator/ice makers also employ some type of built-in air gap as their method of protection.

Residential type kitchen and lavatory faucets, constructed within the US, with integral or auxiliary spray heads, generally do not need additional backflow prevention devices.

General Hose Bibb and Garden Hose Usage

Because of their portability and universal ease of connection, general purpose/garden hoses pose one of the greatest risks for backflow occurrences. In addition, there is a general complacency (underestimation of hazard level), with what hoses are connected to or with what they are left submerged in.

For general applications, the normal way to protect the drinking water system from the hose, and its uses, is to outfit the hose bibb (spigot/valve) with a vacuum breaker. Hose bibbs are available with integral vacuum breakers or vacuum breakers can be purchased separately and screwed directly onto the outlet threads of the bibb. In this case, the vacuum breaker, in turn, has hose threads to connect the hose to. Vacuum breakers are very inexpensive but provide a very good level of protection against backflow.

Every hose bibb, regardless of age or usage, must be outfitted with a vacuum breaker meeting the product standard/listing ASSE 1011 or ASSE 1019.

Vacuum Breakers are considered non-testable and may be installed or replaced by an owner, tenant, property manager or maintenance staff.

Specific Hose Bibb and Hose Applications

Just because someone terminated a water supply line with a hose bibb or hose thread connection does not mean a standard vacuum breaker is an adequate level of protection. The applications where a hose type connection is utilized are too numerous to list, however please use the following guidelines as well as the WSSC Water Plumbing Code Table 5.2 to determine if additional or alternate backflow protection is required:

  1. Hose is used to connect a water utilizing piece of equipment (basically a permanent connection) – backflow protection should be commensurate with the level of hazard.
  2. Hose connection(s) are present in areas where high hazards are present: vehicle repair shops; sewer pumps; industrial processes, etc. – a RP type Backflow Prevention Assembly is required.
  3. To discuss applications not covered here, give the Cross-Connection Program a call.
    Prince George's County (301) 206-8601
    Montgomery Count (301) 206-7932

In-ground, Irrigation/ Lawn Sprinkler Systems

Automatic irrigation systems pose a significant threat to the drinking water system. By their nature, sprinkler heads may reside in a pool of yard/animal waste, pesticides and/or fertilizers. In addition, extreme high pressure air is typically used to winterize (blow out) the underground pipes; this greatly increases the probability of backflow. And because the supply lines are under continuous pressure, and controlled by underground control valves, a typical vacuum breaker is not an appropriate form of protection against backflow. There are two types of backflow prevention assemblies allowed: (1) Pressure Vacuum Breaker (PVB) – ASSE 1020; this assembly must be able to be located outside, one (1) foot above the highest sprinkler head, and no more than five (5) feet above grade at the installed location. (2) When the parameters for a PVB cannot be met, a Reduced Pressure-Principle (RP) - ASSE 1013 shall be installed. Required to be outside, no restriction on elevation of sprinkler heads, and mounted 18”- 24” above grade at the installed location.

PVB may be winterized in place; RP’s must be removed and placed in a warm storage area. Both assemblies require their annual test at the time of spring seasonal start-up.

Installation, repair, replacement and/or annual testing must be performed by a plumbing services firm (licensed plumber). Their plumbers must be at least of the “Journeyman” license level and also possess a separate cross connection technician certification. Do not be afraid to ask for proof!

Hint for owners with irrigation systems: make the testing part of your spring start-up contract. The irrigation firms may be able to procure the most favorable pricing due to their ability to deal in volume with plumbing services firms.

Fire Sprinkler Systems

Fire Sprinkler Systems
Since their inception, commercial fire sprinkler systems have been supplied with water by several different piping and metering arrangements. The following describes the details of each variation:

  1. Limited System (timeless) In this arrangement, water is supplied to a limited number of sprinkler heads directly from the potable (drinking) water system. If the sprinkler head lateral is less than 2’ in developed length(measured from the potable main to a single head) and constructed of material acceptable for potable water, no backflow prote cti on is required. Up to 7 heads can be supplied from a branch system(s) where the largest pipe diameter used is 1 1/2”. Each connection to the potable system shall be protected with an ASSE 1024 DCV backflow device. Co de requires rebuilding or replacement of the device every five years. A tag shall always be hanging from the device identifying installation date, expiration date, or both.
  2. Up to April 30, 2007 and regardless of metering arrangement, fire sprinkler systems were outfitted in one of the following three piping arrangemen ts .
    1. Double Check Valve Assembly (DCVA ASSE 1015) a testable backflow prevention assembly requiring annual testing and reporting.
    2. Single Check Valve a non testable backflow prevention device which requires rebuilding or replacement every 5 years. A tag should always be hanging from the device identifying installation date, expiration date, or both. If no tag is present, the single check valve will be perceived to be past the required 5 year maint ena nce requirement and warrant replacement.
    3. Unprotected system a testable backflow prevention assembly was required based on the following:
      1. ASSE 1015 DCVA fire water is previously metered or a current supervised sprinkler agreement is on record.
      2. ASSE 1048 DCDA unmetered or unsupervised fire water.
      3. Hydraulic Consideration for the impact of adding a Backflow Assembly is the owner responsibility and shall be presented to th e a ppropriate county or city fire official for approval.
  3. May 1, 2007 to February 28, 2019; fire sprinkler systems were outfitted using one of the following methods:
    1. An ASSE 1015 DCVA required where fire water is previously metered, typically by a large outside meter.
    2. An ASSE 1048 DCDA required where fire water is not previously metered, typically when domestic water is/was metered by an inside meter. The 1048 contains two testable 1015 BFPs; one main assembly and the other situated on the by pass feature. In addition, the by pass contains a pre piped meter accommodation. The 1048 was t o be purchased without a meter; WSSC Water supplied and set the meter in this arrangement as a “tattle tale” device to ensure the fire water is not used for any other purpose other than fire fightin g. Within this time frame, the ASSE 1048 Type 2 bypass was introduced by several manufacturers. The Type 2 bypass has a single check in the bypass around the second check module and utilizes the first check mo dule as preservation of double check valve protection for the bypass incorporated into the design of the ASSE 1048 Type 2 assembly.
  4. March 1, 2019 to Present; fire sprinkler systems shall be outfitted using one of the following methods:
    1. An ASSE 1015 Double Check Valve Assembly.
    2. Owner/Engineer option to specify the design preference to install a n ASSE 1048 DCDA. If an ASSE 1048 Type 1 or Type 2 assembly is permitted and installed as the Owner/Engineer design preference, the Owner will be responsible for performing two annual field tests for the life of the ASSE 1048 assembly, maintaining both the pri mary assembly and the bypass check modules, maintaining all assembly and device components, and metering and/or detection of flow shall be th e ongoing responsibility of the building/facility staff.
  5. Non-Standard Fire Protection Systems. Where chemicals are introduced, normally as an anti freeze agent or where the system itself utilizes chemicals to mix with the fire water to create an enhanced fire fighting material, an ASSE 1047 Type 1 or Type 2 Reduced Pressure Principal Backflow Prevention Assembly shall be installed as follows :
    1. Up to February 28, 2019 WSSC requirements were:
      1. An ASSE 1013 RP was required in applications where a 1015 is specified in 3a
      2. .An ASSE 1047 RPDA was required in applications where a 1048 is specified in 3b.
    2. From March 1, 2019 to present:
      1. An ASSE 1013 Reduced Pressure Principle Backflow Prevention Assembly (RPDA) shall be installed.
      2. Owner Engineer option to specify the design preference to install an ASSE 1047 RPDA. If an ASSE 1047 RPDA is specified for installation by the design Engineer, Owner will be responsible for performing two annual field tests for the life of the assembly, maintaining all assembly and/or device components, and metering and/or d ete ction of flow shall be an ongoing responsibility of the building/facility staff.

Booster Pumps

Whether for domestic use, fire protection, or an industrial application, the required backflow prevention assembly or device shall be upstream (ahead of) the booster pumping system.

Heating Systems / Boilers /Cooling Towers/ Chilled Water/ Condenser Water

Where water is connected to a heating or cooling system as a make-up water supply, it must be protected by a RP type Testable Backflow Prevention Assembly - ASSE 1013. This assembly is considered “testable” and must be tested yearly. An air gap at the cooling tower is a sub-standard form of protection due to potential bacteria growth within the spout caused by exposure to contaminated vapors and the extended time in a “no flow” condition.

Dark Room Sinks and Automatic Film Developers

Not a very common item anymore with the advent of digital photograph; photo developers and sinks are certainly a rarity these days. But when connected to the water distribution system, backflow prevention is a must. If connected to a tank or sink, a “non-testable” device (standard no. ASSE 1012), may be utilized. If chemical injection is present or an automatic developer is used, a “testable” assembly (standard no. ASSE 1013), must be installed and special provisions for drainage need to be considered and yearly testing by a plumber is mandatory.

Medical Equipment

Medical/Dental Vacuum Systems, Sterilizers, and other medical equipment utilizing potable water shall be isolated with a RP type backflow prevention assembly – ASSE 1013.

Water Treatment Systems and Filters

In-line cartridge filters shall be isolated with a Dual Check Valve (DCV) – ASSE 1024. Treatment systems incorporating chemical injection, reverse osmosis, de-ionization, etc. shall be isolated with a RP type backflow assembly –ASSE 1013. Ultra-Violet light (UV) treatment systems do not require backflow prevention.

Beverage Dispensers

Carbonated beverage dispenser shall be isolated with an ASSE 1022 backflow device. All other beverage dispensers may use either an ASSE 1022 or 1024 device. Where 1022’s are installed, the area shall be capable of handling the discharge.

Non-Testable Devices

ASSE 1012, 1022, 1024 & 1081 backflow devices shall be re-built or replaced every five years. A tag shall always be hanging from these devices identifying installation date, expiration date, or both. Other non-testable devices are good for the life of the fixture or appliance served or until leakage/failure.

Vacuum Breakers

Pipe applied or spout applied vacuum breakers cannot be subjected to continuous pressure. They must be installed downstream of a water control point and the downstream process must relieve pressure in each off cycle. Pipe applied Atmospheric Vacuum Breakers (ASSE 1001) shall be a minimum of 6” above the highest downstream use and installation of the ASSE 1001 has additional requirements which must be observed. Spill Resistant (ASSE 1056) and Pressure Vacuum Breakers (ASSE 1020) shall be a minimum of 12” above the highest downstream use.

Other Water Uses

Refer to WSSC Water Plumbing and Fuel Gas Code, Chapter 5 & Table 5.2 or consult with a licensed plumber regarding proper connection and protection requirements or contact a WSSC Water inspector by phone or email: 301-206-8886 or

Suitable Areas for Installation and Adequate Consideration for Drainage

Backflow Assemblies shall be readily accessible and Backflow Devices shall be accessible. Assemblies and Devices that are designed to discharge shall be installed in areas suitable for that condition and it is highly recommended that consideration be given to an Assembly’s potential catastrophic failure and subsequent large volume of sustained discharge. Where adequate drain sizing is impractical, consideration should be give to an automated detection-initiated shut-down system.

Best Management Practices (BMPs)

Understanding and respecting the risk of water contamination is a great start, when in doubt, seek help. Basic guideline: every water outlet needs some form of protection; get to know what is needed. Have “non-testable” backflow devices rebuilt or replaced at the intervals described above. Have “testable” backflow assemblies tested yearly and each rebuilt or replaced as needed.

Last Modified: May 2, 2023, 2:14 pm EDT